Abstract: Models for the amplitude fluctuation of a line-component spectrum of ship radiated noise and ambient sea noise have discussed in this paper.When the signal model of line-component spectrum is taken to the sum of a sine-wave and narrow-band Gaussian white noise,the output fluctuation statistics for a narrow detector are found to follow a non-central chi-square distribution with ZBT degrees of freedom.The variance is equal to the sum of the variance caused by source characteristics and propagation processes and the processor's variance.On the other hand,the model of ambient sea noise is taken to a stationary white-Gaussian noise,the output fluctuation statistics are found to obey a chi-square distribution with 2 BT degrees of freedom.Its variance'is determined only by the processor itself.The experiment data from the sea measurements is coincided with the theory computation.